The present disclosure relates generally to electrochemical machining (ECM) and, more specifically, to a drilling tool for use in forming a continuous, variable geometry bore hole within a conductive work piece.
Rotary machines, such as gas turbines, are often used to generate power with electric generators. Gas turbines, for example, have a gas path that typically includes, in serial-flow relationship, an air intake, a compressor, a combustor, a turbine, and a gas outlet. Compressor and turbine sections include at least one row of circumferentially-spaced rotating buckets or blades coupled within a housing. At least some known turbine engines are used in cogeneration facilities and power plants. Engines used in such applications may have high specific work and power per unit mass flow requirements. Moreover, the efficiency of gas turbines is directly proportional to the temperature of exhaust gas discharged from the combustor and channeled past the rotating buckets or blades of the turbine. As such, the extreme temperatures of the exhaust gas generally require the static and rotating turbine airfoils to be manufactured from high temperature-resistant materials, and to include cooling features therein.
For example, turbine blades are typically cooled by channeling compressor discharge air through a plurality of cooling channels extending through the turbine blades. At least one known process of forming the cooling channels in the turbine blades is shaped-tube electrochemical machining (STEM). STEM is a non-contact electrochemical machining process that utilizes a conductive work piece (i.e., the turbine blades) as an anode, and an elongated drilling tube as a cathode. As the conductive work piece is flooded with an electrolytic solution, material is oxidized and removed from the conductive work piece near the leading edge of the drilling tube. STEM is generally effective at forming straight cooling channels having high aspect ratios within a conductive work piece, such as a turbine blade. Electrochemical machining techniques have also been developed for forming non-linear cooling channels within turbine blades. However, contact or rubbing sometimes occurs between a drilling tool and side walls of the cooling channels when guiding the drilling tool through the non-linear cooling channels, thereby decreasing the service life of the drilling tool. Moreover, at least some known turbine blades are fabricated from material that is not easily oxidized during an electrochemical machining process such that wear of the drilling tool is further exacerbated.